Light meter



April 1o, 1945. N, .LLER 2,373,327

LIGHT METER f Original Filed April l, 1940 3 Sheets-Sheet 1 pril l0, 1945. N, MlLLER l 2,373,327

LIGHT METER Original Filed Abril 1, 1940 3 Sheets-Sheet 2 MIIIIIIIIIIIIIIIIIIIHI PUPIL DIA. mm

BRIGHT/1555 1 CA IvD/ E5 PEE SQFT.

Vpril l0, 1945. N. MILL/ER LIGHT METER Original Filed April l, v1940 3 Sheets-Sheryl 5 Patented Apr. 1.0, 1945 Original application April 1, 1940, 'Serial No. 327,238, now Patent No. 2,206,292, dated Septomber 22, 194.2. Divided and this application September-2, 1942,I Serial No, 457,063

'15 claims. (ci. ax-f2s) This application is a division oi application Serial Number 327,238, led April 1, 1940, and relates more specically to the determination of light intensities by the measurement of the pupillary diameters oi the human eye, as it is affected by the light falling upon it.

For elements and mechanisms shown on the drawings, but not `described in this specification, reference is to be had to my issued vPatent No.

2,296,292, september 22, 194,2. I

In thepresent invention improvements are.

provided whereby the light rays which reach and inuence the pupil of the eye, are deiinitely limited to a ileld of rays, which correspond. to the eld covered by the camera objective. The eifect of this restricted light iield upon the pupillary opening is that produced by the average of the light intensities proceeding from; all points 1oi the obiectfleld, so that by this means the proper exposure required by any given scene may be accurately determined.

Another improvement consists of ilxed reiiec- --t'ors positioned in'such a way, that light rays l proceeding irom th'eobiect ileld are intercepted by said reiiectors, and directed upon the eye, so that the light falling upon the pupil is sumcient to'produce pupillary imageswhich maybe clearly observed even in dim light.

A further improvement consists oi a focusing means whereby the image forming lensand reflectors are adapted to be shifted in .an axialdirec tion, so that the instrument can be adjusted 'to yield sharp pupillary images either for normal or ior detective vision, and this is accomplished without changing the position of the instrument relative to theobserver's eye.l A vision dial is provided with ,a scale, ior setting the instrument corresponding to near vision, normal vlsion, and

far vision; intermediate positions are also indicated so that the instrument may be preset, ir

-'desired A For callbrating the instrument an adiustable screw is provided with'graduation marks, and by means o! this screw. the langular relation between the' image forming reiiectors may be altered to correspond to the individual variation oi the pupillry diameters.

It is to be understood that the principles oi pupillary measurements herein disclosed are not tions for these are'A related to a. predetermine pupillary opening for each individual. e l

To the attainment o i these ends and the aceomplishment. oi other new and useful objects as will appear, the invention consists inthe features of novelty in substantially the construction, com'- binatiou and arrangement oi the several parts,

hereinafter more iully described and claimed and shown in the accompanying drawings, and'in lo which l Figure 1 represents' an enlarged top view oi theinstrument with the exposure meter andvrange iinder dials removed tomore Vclearly show the construction., e

u more 2 is a sectional .view tekesmngune Figure 3 is a sectional view taken along 3-3'Flgure 2.

Figure 4 is a partial-section taken along. line Figure 5 is a partial section taken along line 5'-5 Figure 1. l

Figure 6 is a partial section'taken along-line il llgure'lisatoliviewoitheinstrumentshowing the exposure meter'and the range 'finder dials imposition.

Figure 8 is airont elevation of Figure A7. e Figure 9'is a side elevation o! Figure 7.

Figure 1o is s partiel bottom'view snowing ,the

vision scale Figure 11. `is a schematic horizontal section showing the path oi rays'to the exposuremeter 4 and the range finder.

35 Figure i2 'is s partiel-iront elevation et Figure -'rnnure vis is epsrusi side view of rigore `'1 1. Figure 14 is a partial schematic sectional view" o similar to Figure 11 showing the reiiectio'n of rays v from a parabolic type reiiector.v

'rime 15 is s parmi sise 'view of Figure 14.'

Figure 16 is. an end view oi the re'ector shown in Figure il'.v

u Figure 1v is e diagrammatic view showing the appearance of the images oi the eye and ci the pupillary images.

Figure 18 is a sectional diagrammatic view-ici the lens and reflector combination and the path' restricted to exposure determinations in the nels. so' 0f. the rays 10mm' the'ruvillary imsesoi photography, but have other usei'ulapplications, as ior example. in determining the light intensities or srtiiicial illumination, which are necin the certain tasks, such ss reading, sewing, etc., since theoptimum condb rieures 19. 2o ena-'21 show the two 'pupille-ry intiilages'in various positions relative to one an- 22 shows thealinement oi thepupillaiy ih imageswhen the' pupil is belowthe 'optic axis.

tim' A reected from it to the reiiector 38, It is to be Figure 24 is a graph oi! the pupillary reaction I to varyinglight intensities.

vvIn Figures 1, 2 and 3, the numeral In represents a casing which is made preferably of a plastic material such as Bakelite. Inside this casing are mounted the component parts of the exposure meter. The lower right side of the cas.- ing is provided with an oval shaped opening I5, Figures 1, 'l and 8, adapted to accommodate the right eye, which is used in operating the exposure meter.

A transparent arcuate member I8 is provided to seal the oval opening. and to allow the light rays to pass to illuminate the pupil oi the eye. On the two sides ofthe oval shaped opening are positioned the reiiectors 22 and 23, Figures 1, 2, 3, 11, 12 and 13. The right eye and its pupil E shown schematically in Figures 11 and 13 at 24; the numeral 25 represents the direct rays which reach the center of the pupil, and 2B represents the.

. rays reflected by the reector 23 reinforcing the direct rays in illuminating the pupil. These groups of rays 25 and 26 illustrate how the available'srays are limited to a deilnite angle by the edge of the casing on the right side, and by the upright part of the -:frame member 21 on the leit side of the opening. The numeral 28 is an arcuate transparent member for sealing the openings on the two sides of the upright frame member 21.

A similar group of rays (not shown) reaches the pupil through the opening on the left side of the member 21. In Figure 13, 29 shows the limitation of rays in a. vertical plane, so that when the instrument is pointed at an object. sky light will be excluded from reaching the eye. In ,Figure 14 a parabolic reiiector 32 further restricts the angle of the reected rays. since those that noted that all rays proceeding from the illuminated pupil undergo reections at both of the reflectors before they are directed back into the pupil, causing the two images to become visible to the eye,

The function o1 the lens 31 in front of the reiiectors is to magnify the pupil images, and does not aiect the principle of double image formation as above described. By a suitable choice of the position and of the focal length of the lens 3l, the magniiication ofthe'pupil images, and

- their distance from the eye, can be predeter reach the center of the pupil are the parallel groups of rays 30.

In Figures 14, 15 and 16, the reflector 32 is shown provided with flanges 33 so that a transverse section of the mirror is U shaped as appears from the end view, Figure 16.

In Figure 15, rays 3| show the iianges 33 reflecting rays to the pupil which. however, are

limited to a small angle. Theserays are additional to the direct'rays which reach the pupil, as shown-at 29, Figure 13. The operation of the exposure meter depends upon the response of the pupil opening to the stimulus induced by the light which is incident upon the eye. This rponse is. measured by means o1' two enlarged virtual images of thel illuminated pupil, formed by a lens and double reiiector combination.

To simplify the description oithe functions of the double reilectors, suppose that in Fig. 18 the lens 31 is removed. Then, if the two reectors 38 'back intothe pupil. Thesecond pupilfimage isrormedinasimilarwambutbyrasswhichmined.

-If the angle. between the reilectors 38 and 33 is so adjusted that the two images just touch one another, as at P'Q", then it can be shown that the magnitude of this angle is dependent upon the diameter of thek pupil, so that this angle becomes a measure of the pupil diameter.

In Figure 18, PQ represents the illuminated pupil, and the paths of the ree'cted rays are shown as proceeding fromthe point of tangency of the enlarged virtual images QP' and Q"P" of the pupil. The appearance of these images, as seen by the observer, is shown in- Figure 20. If the reectors 38 and 33 remain in their adjusted positions of Figure 18, and the light intensity incident upon the pupil diminishes, the -pupil dilates and its virtual images will be overlapping as shown in Figure 19, the-degree of incident upon the pupil. f

Figure 22 .shows the position of the pupil images when the pupi1 Q is moved laterally with respect to the optic axis. The pupil Aimages in this case will appear to the observer as shown in Figure 23.- An important feature of I'the optic system herein disclosed is that the lateral movement of the pupil with respect to theoptic axis, does not disturb the relative positions or alinement of the pupil images, as it appears to the observer, which greatly facilitates the use of the ixistrumv ent,

Figure 24 shows a graph of the pupillary reac- -tions with respect to various light intensities.

In the present invention the lens and reflectors are movable axially toward or away from the Apupil in order to obtain a sharp outline of the pupillary imagas, corresponding to near vision, or -far vision, o r any intermediate vision of the observer. In Figure 1, on the top of the casing l0, `a. large round opening is provided and Ythrough this opening the frame member 21 is assembled into the casing. The lower end ofthe frame member 21 forms a'. horizontal extension 34, Figures 1, 2 and 3, which extension is provided with a slot 35 and in this slot is mounted for sliding motion a member 36, which supports the convex lens 31, the reector 38, and the pivoted reilector 39. Member35 is held frictionally by a two-pronged spring 40 which exerts pressure between the sliding support 33 and the under side of the slotted frame extension 3l. The underside of the sliding support 3B is provided with a transverse slot Il which coloper'- altes with astud I2, Figlrresl and 3. The'stud are incident rst-uponthe reflector 39, and then .7571, 2, 3 and 10, which is mounted for rotation through a hole in the underside of the casing at 44,'Figure 1.

An arcuate slot 45 also on the underside ofthe casing, provides clearance for the movement of the stud 42 when the knurled wheel 43 is turned v 'by the ngers for moving the lens 4l together with the reectors 38 and 39toward'or away from the eye of the observer. In Figure the knurled wheel is shown provided with a vision scale so that the wheel may Ibe preset with respect to the reference mark 46 on the casing l0, according to the lower reflector 38 which is somewhat narrower than the upper reilector 39, as shown in Figure 2, so that the reflector 3911s pivotally movable with respect to the reector 38. One side of the reector holder extends rearwardly and is provided with a pin 52, which is held in contact with an elongated cam member 53 by a springv 54 which.

is anchored to a hook projecting from the support 36, Figure-3. As the support 36 is moved by thel rotation of the Wheel 43, the pin 52 slides member 53, thereby imparting a small rocking motion to the reflector 39. The two virtual images of the pupil are brought into a position of tangency by the rocking movement of one of the.

reectors, said movement being a measure of the pupil diameter, and hence, indicates the correspending light intensity falling upon the eye. Hence, in moving the lens and reector combination toward or-away from the pupil for bringing the pupil images into a sharp focus, it is important that this relation of tangency be maintained, and the small rocking motion imparted to the reector 39 as above explained is for the purpose of maintaining the relation of tangency of the pupillary images during the focusing operation. If the user wears spectacles or glasses, readings may be .taken b'y holding the instrument in contact with the'surface of the glasses, but in this case the lens and reilectors must be moved toward the eye in order to compensate for the distance between the pupil and the outside surface of saidglasses. The free end of the cam member 53 is likewise provided with a slightly tapering surface 53h, co-operating with the pin 52 for imparting to the reflector 39 a compensating movement in the process of focus--l ing in connection with the use of glasses.

To bring the pupillary images into. a. position lower part of the loop, while the upper part of the loop presses against the underside ofthe head of the screw. The upper part of the loop is oii'set, terminating in a cupped lip 60, which rests upon a circular cam surface 6I, which is an integral part of the knurled disc 82. It will be evident from Figures 3 and 6, that as the knurled disc is rotated in a horizontal plane, the cam sur--l face I will impart a vertical motion to the cupped lelongated cam 53 will be raised or lowered with respect to the cam surface 6I and thereby the angular relation of the reflectors 38 and 39 may be adjusted, for the purpose of calibrating the instrument.

In Calibrating, the reflectors are adjusted to register the tangency of the pupillary images in a predetermined light condition and corresponding to the average size pupil. vAt the calibrated point the screw head59 is marked with a dot 64, Figure l, opposite a. reference mark 65 upon the cupped lip. The dot mark is preferably made with some paint or pigment, and its purpose is to fix the position of the calibration. The screw Y v i head 69is further provided with graduated marks upon the slightly tapered surface 53a of the cam of tangency, the cam memberA 53, Figure v3, is

` moved vertically, for imparting to the reflector 39 therequired rocking motion. The cam'mem ber 53 is provided with a downward projection .39. Figure, which slides in a slot in the frame p member 34. Integral with the cam member is the upward projection 56 which slides in a slot of an upper horizontal extension v51 of the frame member 21, Figures l, 2, .3 and 6. As shown in Figure 6, the upward projection 56 is provided with a. .loop formation 59, which is made of a resilient material, and functions as a spring. A screw 59, Figures 1, 3 and 6, is threaded into the as shown in Figure 1 for the purpose of altering its positionJ a known amount,l in case the variation from' the average pupil in an individual case makes this desirable.

The disc 62 is provided on its underside with an arcuate groove 36, Figure 3, which serves as a race for three spaced ball bearings 61, 68 and 69, Figures 1, 2 and 3. The balls are supported in cup formations on the upper horizontal frame member 51, as shown at 69, Figure 3. The purpose of the ball bearings is to give proper circumferential support to the knurled disc 62 and by its antifriction properties to facilitate the operation of the knurled disc by the lingers; iurther, the relation of the cam surface 6i to the race 66 opposite it, can easily :be fabricated with a-lhigh degree of accuracy and it is this factor which controls the rocking motion imparted to the reflector 39. A circular -plate 19 rests on a recessed shoulder of the disc 62, Figure 3, and this plate is provided with a small projection 1 I,

Figure '1, which secures said plate on the disc 62.

against relative motion, so that when the knurled 4disc 63 is rotated, the plate 10 willmove as if integral with it. At its center the plate 1o is provided with a circular aperture which ts loosely around the cylindrical body 12 of a knob 'I3 while a shoulder 14 on the knob 13, Figures 3 and 5,

bears down on the edge of the circular aperture g so that by the plate 10 and the knob 13 'the knurled disc 62 is securely held in place.

.The knob 13 is fastened tothe frame member 51 by means of a stud 15 which lits in to a hole provided in the knob 13 The stud 15 has a groove 16 and opposite this groove the knob is provided with a'recess 11, Figures 3, 4 and 5, which accommodates a horseshoe spring 18 so that when the knob is forced down-upon the stud Vthe -Y spring `snaps in the groove on the stud and therefby retains. the knob in place. A projection 19,.

Figure 5. fits into' a hole in the frame member 51 and prevent the knob from turning. The upper surface of the knob ll is made concave and serves as a finger rest to facilitate the holding of the instrument, and the turning of the disc 82. In

v Figures 1 and 3 a projection 80 in the path of a similar projection 80a on the disc 62 acts as astop. limiting the rotation of the disc in iboth directions.

In Figure 7 the circular plate 10 is shown with a time scale on its outer edge. Another circular plate 8| disposed above the plate 'I0 is provided with a series of stop numbers indicating the objective aperture, which are adjacent to and are co-ordinated with the numbers of the time scale on plate 10, so that when the disc 82 is adjusted to cause the pupillary images to be brought into alinement, the 'adjacent pairs of numbers on the time and stop scales will indicate the correct shutter speed, and the corresponding objective aperture. Since the numbers on the time scale correspond to definite pupil diameters, which in turn are influenced by the light intensity, it follows that the numbers on the time scale can also be interpreted in terms of illumination or light values. During the operation of the disc 82 the stop plate 8| remains relatively fixed.'

The plate 8| is also provided with film speed numbers indicated in Figure 7 as Weston speed numbers, two of which are visible through an aperture 82 on a plate 88 disposed on top of the plate 8|, Figures 3. 5 and 7. The plate 83 extends under the head of the knob 13, and is formed with a downwardly projecting flange or rim 84 which is spun or crimped around a resilient friction ring 85 in such a manner that the plate 8| will be held frictionally but movable between the plate 88and the friction ring To set the stop scale to a desired film speed value, the plate 8| is rotated with respect to the aperture 82, and a projection 88 on the plate 8|,

Figures 7 and 9, is provided to facilitate this operation. Plate 83, Figure 7, has a semi-circular part 8l cut away and the plate 8| has a similar circular portion 88 cut out in such a way, that the plate 8| may be rotated to bring the portion 88 opposite the out out 8l, thus forming at that point a circular opening which is just above the adjusting screw 58, Figure l, and is the means by which this screw is made accessible when such an adjustment is desired. The plate 10 is provided with a similar hole or opening opposite thecut out 81, as shown in Figure 3.

'I'he plate 88 'is spun or crimped around the frictionring 85 in such a way that relative mo tion between them is prevented, while the plate" 8| is frictionally supported between them, and carried along by them.

In Figure 17 is shown'the appearance of the f images of `the eye when the pupillary images Q' which co-operates with the cam A coml pression spring |02, anchored on the casing, presses on the lever, holding the roller |80 in contact with its cam. The cam |0| is supported for free rotation upon a stud |08 which is fastened to the top of the casing 92.

Another lever 9| is provided with a stud |06 which slides in a groove in the upper wall of the casing, so as to prevent its movement longitudinally. A roller |01 opposite the stud |06 co-operates with the cam |08, and a. spring |09 anchored in the casing I0 presses against the lever 9|, holding the roller |01 in contact with the cam |08. The cams |0| and |08 are integrally supported upon Atheir common stud |03, and thereby the movements of the reector lever arm 88 and of the lever 8| are co-ordinated. The lever 8| is provided with a slot at its free end, which fio-operates with the pin 90 on the under side of a downwardly projecting U shaped lug 89, which is part of the friction ring B5. Fig. 5, and by this means movement is transmitted to the plates 8| and 83 for influencing the relation of the time and stop scales in accordance with the settingv of the reector 94, by the operations of the cams |0| and |08.

What I claim as new is:

1. In combination Awith a light meter, a lens, means for positioning said lens relative to the pupil of the eye, two reflectors, their planes forming an approximate right angle and cooperating with said lens, for forming two virtual .images of the pupil, means for altering the angle lbetween the reiiectors for bringing thedmages of the pupil into tangency, a support.` for said reflectors, and means for moving said support along the optic axis. 2. In combination with a light meter, a lens, means for positioning said lens relative to the pupil of the eye; two reflectors, their planesv forming an approximate right angle and co-operating with said lens, for forming two virtual images of the`pupil, means for altering the angle the angle between the reflectors for bringing the images of the pupil into tangency, a support for the lens and said reflectors and means for sliding said support along the optic axis; a disc mounted for rotation, end connection between the disc and said support for sliding said sup-" port along the optic axis'by the operation of said disc.

4. In an exposure meter adapted to measure the diameter of the pupil of the eye, a lens, two reflectors, their planes forming an approximate right angle and co-operating with. said lens, means for positioning` thelens relative to the pupil, a casing having an aperture for the en- .trance of light rays to illuminatel the pupil, means for limiting such rays to a predetermined angle,

. and provision for altering the angle betwen the reflectors to bring the two virtual images oi the pupil, formed by the lens and the reflectors, into a position of tangency.

5. In a light meter adapted to measure the diameter of the pupil of the eye, a lens, ltwo reflectors,their planes forming an approximate right angle and co-operating withsaid lens, a

casing for the lens and said reflectors and means for positioning the lens with respect to the pupil of the eye, said casing having an aperture for the entrance of lightrays and a parabolic type reflector xed on one side of the aperture adapted to reiiect rays within a predetermined eid for the illumination of the pupil, and means for altering the angle between said reliectors to bring A the two virtual images of the pupil, formed by f casing for the lens and said reliectors and means for positioning the lens with respect to the pupil oi the eye, said casing having two apertures on opposite sides of thepptic axis for the entrance of light rays, and two reflectors fixed on the sides of the apertures adapted to. reiiect rays` within a predetermined angle for the il lumination of the pupil, and means for altering the angle between said reectors to bring the two virtual images of the pupil, formed by the lens and the reflectors, into a position of tangency.

7. In combination with a light meter, a lens.

I means 'for positioning said lens relative to the pupil of the eye, two reflectors, their planes forming an approximate right angle andcooperating with said lens for forming two virtual images oi' the pupil, a support for the lens and said reectors, and means for sliding said support along the optic axis; a pivotal mounting for one of the reflectors on said support, and a cam member adapted to impart a rocking movement to the .reector about its pivot during the sliding Vmotion of said support for bringing the images of the pupil into tangency.

8. In a light meter iorl estimating illumination by the measurement oi' the diameter of the pupill oi the eye, two reilectors; a. screw, and means for adjusting the angular relation oi' the reflectors by said screw in accordance with apredetermined pupil diameter and provision for indicating said adjustment on the screw; a graduated scale for said screw, whereby the angular relation of 'said reectors may be readiusted in accordance with the variations of the pupil diameters of the' eye. i

9. In an exposure. meter, a scale of time values, a scale of stop values and means' for adjusting the relation between said scale two reectors, their planes forming an approximate right angle and ineens for viewing the images of the pupilof the eye formed by said reflectors, and provision for altering the vangle of the reilectors to bring the pupil images into tangency by the adjustment of said scales.

10. In an exposure meter, a scale of time values. a scale ci' stop values and means for adjusting the relation betweensaid scales; a scale of film speed values. and means for modifying thelrela- -tion between the time and stop scales in accordance with a predetermined lm speed value; two

reflectors, their planes forming an approximate right angle, and means for viewing the images of the pupil of the eye formed by said reiiectors, and provision for altering the angle of the reliectors to bring the pupil images into tangency by the adjustment of said scales,

1l. In a light meter, two reflectors, their planes 'forming an approximate right angle and means for positioning said reilectors relative to the pupil of the eye for viewing the pupil images formed by said reilectors; means for` altering the angle of the reflectors to bring the pupil images `into tangency; means for moving the reflectors toward or away from the eye for shifting the pupil images into the position ofdistinctvision, and provision for imparting a compensating movement to one of said reiiectors to maintain the tangency of the pupil images.v

12. In alight'meter, two reiiectors, their'planes forming an approximate right angle and means for positioning said reflectors relative to the pupil oi the .eye for viewing the pupil images formed by said reliectors; means for altering the angle of the vreflectors to bring the pupil images into tangency; means for moving the reiiectors with respect to the pupil, and a scale indicating the position o! the reflectors for th`e point of distinct vision.

13. In a light meter, two reflectors, their planes forming an approximate right angle and adapted to form images oi' the pupil of the eye; means for viewing said images directly, or with glasses; means for altering the angle between the reilectors to bring the pupil images into tangency;

means for moving the'refiectors with respect to forming an approximate right angle and means for positioning said reilectors relative to the pupil the pupil, a scale indicating the position of the reiiectors for the direct vision of the pupil images, and another scale indicating the position of the reflectors for viewing the pupil images with glasses.

. 14. In a light meter, two reflectors, their` planes forming an approximate right angle and means for positioning the reilectors with respect to the pupil of the eye for viewing the images ot the pupil formed by said reilectors; means for altering the angle between said reliectors for bringlng the pupil images into tangency, and provision for measuring the magnitude of said'angle.

15. In a light meter, two reilectors, their planes of the eye; a case for said reiiectors having an aperture adapted for the entrance oi' light for innuencing the diameter of the pupil; means for altering the angle of said reflectors for bringingv the pupil images into tangency, and a co-operating scale device tor indicating the light values incident upon the pupil.

.- NICHOLAS MILLER.. 

